SIL-rated process safety functions are now commonplace, and as an extension of this many users are specifying SIL-rated fire (and gas) safety functions. Perhaps this is without an adequate understanding that there are significant differences in the design and implementation of fire (and gas) safety functions – differences that can make it difficult to achieve even SIL 1 safety performance.
This paper will discuss these differences and their impact on achieving safety performance; then it will explore the impact of recommendations made in ISA TR84.00.07-2010: “Guidance on the Evaluation of Fire, Combustible Gas and Toxic Gas System Effectiveness”; and finally, offer a method to manage fire and gas risk without the need for SIL-rated fire and gas safety functions.
IEC 61511 acceptance and adoption varies around the world, but in the UK the Health and Safety Executive (HSE) regards it as close to law. The HSE's IEC 61511 committee member Simon Brown explained: "IEC 61511 is becoming well accepted as the standard of good practice for safety instruments systems in the process sector. It's certainly not a legal requirement in itself, but the requirement to implement good practice is a legal requirement."
The acceptance of IEC 61511 has meant that SIL-rated process safety functions are now commonplace and, as an extension of this, many users are specifying SIL-rated fire (and gas) safety functions. The aim of the paper is to demonstrate that there are significant differences in the design and implementation of fire (and gas) safety functions; and that these differences can make it difficult to achieve even SIL 1 safety performance. This paper takes a ‘high-level’ look at the issues related to SIL-rated Fire (and Gas) safety functions. This means that the focus will be on practical concepts and common sense rather than an academic treatment of the subject.